Effects of Rice Farming Practices and Fertilizer Application on Water Quality of the Mahayahay-Kitcharao Small Reservoir Irrigation Project

Authors: Emmalyn E. Montiza; Romell A. Seronay
Effects of Rice Farming Practices and Fertilizer Application on Water Quality of the Mahayahay-Kitcharao Small Reservoir Irrigation Project
DOI
10.25125/ijoear-may-2026-1
DIN
IJOEAR-MAY-2026-1
Abstract

This study examined fertilizer application practices and their association with nutrient concentrations in irrigation water of the Mahayahay–Kitcharao Small Reservoir Irrigation Project (KSRIP) in Agusan del Norte, Philippines, during the dry season. Nitrogen (N), phosphorus (P), and potassium (K) levels were assessed across upstream, midstream, and downstream locations using a descriptive-comparative design integrating survey data from 64 rice farmers and laboratory water analysis. Survey results showed 78.1% of farmers were ≥50 years old (mean 56.4 years), with average farming experience of 22.3 years; 79.7% were tenants, and 93.8% used only inorganic fertilizers, applied twice per season via broadcast method. Laboratory analysis revealed N concentrations of 0.0075 mg/L (upstream and midstream) and 0.3317 mg/L (downstream). P ranged from 0.1567 to 0.2800 mg/L, and K from 0.7833 to 0.8167 mg/L. Kruskal–Wallis tests showed no significant differences in N, P, or K among sites (p>0.05). All N and P values were within DENR allowable limits for irrigation water (N: 14 mg/L; P: 1 mg/L). Potassium has no established regulatory standard. Despite intensive uniform fertilizer use, dry-season nutrient concentrations remained within regulatory thresholds without significant spatial variation. Continued monitoring and improved fertilizer management are recommended.

Keywords
irrigation water quality nutrient accumulation rice farming practices fertilizer management agricultural sustainability
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Introduction

Irrigation development is critical for increasing agricultural productivity and food security in developing countries [1]. In the Philippines, small reservoir irrigation systems stabilize crop production during dry seasons, but their long-term sustainability depends on responsible nutrient management [2]. Excessive or poorly timed fertilizer application can lead to nutrient losses through runoff and leaching, accumulating within irrigation systems [3]. Nitrogen, phosphorus, and potassium—the primary macronutrients in rice cultivation—are particularly concerning when applied in conventional flood-irrigated systems [4]. In Agusan del Norte, the Kitcharao Small Reservoir Irrigation Project (KSRIP) supplies irrigation water to approximately 550 hectares of farmland. As fertilizer use intensifies to meet production targets, assessing whether nutrient concentrations remain within regulatory limits (DENR Administrative Order 2016-08 and 2021-19 for Class C fresh surface waters) becomes essential. Dry-season conditions with reduced water volume may concentrate nutrients, potentially creating spatial differences among upstream, midstream, and downstream sections.

Conclusion

Rice farming in the Mahayahay-KSRIP is characterized by experienced, older, smallholder tenants who rely uniformly on inorganic fertilizers applied twice per season via broadcast method. During the dry-season sampling period, nitrogen, phosphorus, and potassium concentrations did not differ significantly among upstream, midstream, and downstream locations, and all measured N and P levels complied with DENR irrigation water standards. Therefore, the null hypothesis of no significant difference in nutrient concentrations across locations could not be rejected for any of the three nutrients. Although a descriptive increase in downstream nitrogen was observed, it was not statistically significant. The absence of spatial differentiation suggests that current fertilizer practices have not led to measurable nutrient accumulation within the irrigation network under dry-season conditions. However, continued monitoring is essential to detect potential long-term changes. Current fertilizer practices, under dry-season conditions, do not appear to cause regulatory exceedances, but continued monitoring is warranted.

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References
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